The present invention is generally in the field of biological control of insect pests, specifically in the area of use of entomopathogenic fungi in an infection chamber for the control of insects.
There are many varieties of insects that cause major economic losses in agriculture and spread disease among human and other animal populations. The majority of approaches to control of these insects use pesticides. Unfortunately, pesticides are expensive and generally hazardous to the environment, particularly if effective for more than a very short term. Further, there is a tendency among the treated insects for resistant strains to develop, which requires the use of large quantities and different chemicals to treat. The use of chemical insecticides also results in the destruction of non-target biological control agents.
Insect pathogens are a possible alternative to the common use of highly toxic chemical insecticides for the control of insect pests. Fungi are one of the promising groups of insect pathogens suitable for use as biological agents for the control of insects.
Fungi are found either as single cell organisms or as multicellular colonies. While fungi are eukaryotic and therefore more highly differentiated than bacteria, they are less differentiated than higher plants. Fungi are incapable of utilizing light as an energy source and therefore restricted to a saprophytic or parasitic existence.
The most common mode of growth and reproduction for fungi is vegetative or asexual reproduction which involves sporulation followed by germination of the spores. Asexual spores, or conidia, form at the tips and along the sides of hyphae, the branching filamentous structures of multicellular colonies. In the proper environment, the conidia germinate, become enlarged and produce germ tubes. The germ tubes develop, in time, into hyphae which in turn form colonies.
The fungus Metarhizium anisopliae is an example of a fungus that infects certain species of insects. This fungus has been administered to insect pests by a number of methods, including direct spraying, injection, and by the application of the fungus to the plant material on which the insect lives or feeds. In some insect species, infection with the fungus has been shown to result in death. In one species, infected individuals were able to transmit the fungus to non-infected members of their colony. Metarhizium anisopliae is one of the most widely studied fungus for biological control of insects.
The limitation of the majority of the prior research using fungal pathogens of insects is that it has been conducted under laboratory conditions, which are quite different from the conditions under which the insects are actually found. In most reported cases, death of the treated insects has been achieved by ingestion or injection of very large quantities of spores, which may be toxic in and of themselves. In other cases, infection was achieved by rolling the insect in a test tube containing large quantities of fungal spores. It is clearly impractical to use such methods commercially. Moreover, government regulations would make it difficult to register a fungal insecticide which necessitates the random release of large quantities of fungal spores in areas of insect infestation, particularly in areas in which people or food could be contaminated. No one has yet developed a consistent and commercially viable way of infecting insects and assuring that the fungal inoculum is widely spread.
Blattella germanica (the German cockroach) and Periplaneta americana (the American cockroach) are ubiquitous throughout the world. They have been implicated as vectors of several human disease agents. There are few reports which address the ability of M.anisopliae to infect cockroaches. Gunnarsson, S. G. S., J. Invertebr. Pathol. (46)3,312-319, (1985), for example, has shown that Periplaneta americana exhibits a defense reaction (nodule formation) to the injection of M. anisopliae conidia. Further, there are a number of insect species which are not infected by contact with entomopathogenic fungi.
Control of the house fly is of major economic importance throughout the world because of public health concerns. The fly has the potential to mechanically transmit a wide variety of human pathogens, as reviewed by Bida Wid, S. P., J. I. Braim and R. M. Matossian, Ann. Trop. Med. Parasitol. 72(2): 117-121 (1978). The fly can also be annoying to people, livestock and poultry, to the extent that it even decreases time spent by animals in feeding, thereby decreasing feed efficiency.
A review of the literature reveals the scarcity of pathogens that appear to offer potential to control M. domestica. The bulk of scientific literature on associations of pathogens with house flies refers to isolated reports of diagnosis of dead flies or laboratory studies without practical, short-term applications. Most fungal infections of flies appear to be innocuous, as demonstrated by the isolation of the fungi Aspergillus niger, A. flavus, A. ustus and Mucor racemosus from pupae or adults of M. domestica by Zuberi, et al., Pakistan J. Sci. Ind. Res. 12, 77-82 (1969). There was no evidence of significant effect on the fly populations.
It is possible to infect adult house flies with fungi under certain laboratory conditions, leading to death of the infected flies. For example, Aspergillus flavus was pathogenic to M. domestica when the insects were fed high concentrations (up to 1.times.10.sup.9) of fungal spores, presumably due to toxins in the spores. Mortality after seven days of exposure was 57%; mortality was 100% twenty-one days after exposure. One hundred percent mortality occurred in flies seven days after they were anesthetized and placed in contact with fungal spores, as reported by Amonker and Nair, J. Invertebr. Pathol. 7:513-514 (1965). Dresner, J. N.Y. Entomol. Soc. 58:269-279 (1950), also reported that an isolate of the fungus Beauveria bassiana infected adult M. domestica when the insects were exposed to a dust of germinating conidia adhered in a nutrient medium. The fungus was also infective to flies when the insects were exposed to a dish of milk containing fungal conidia.
D. C. Rizzo conducted studies, reported in J. Invert. Pathol. 30, 127-130 (1977), on the mortality of flies infected with either Metarhizium anisopliae or Beauveria bassiana and determined that the time to death after infection was independent of age. Flies were infected by rolling them for ten minutes in four-week-old fungal culture slants until they were completely exposed to the spores, then maintaining them in humidity chambers. As noted by the author, in reference to the infecting fungi, "these pathogens have never been reported as having caused mycoses in fly populations in nature" at page 127.
In 1990, however, D. C. Steinkraus, et al., reported in J. Med. Entomology 27(3), 309-312, that Musca domestica L., infected with Beauveria bassiana had been found on dairy farms in New York, although at a prevalence of less than 1% (28 out of 31,165). Isolates of the fungi were infective for laboratory raised flies, but the low naturally occurring incidence led to the conclusion by the authors that "it seems unlikely that these infections represent naturally occurring epizootics within house fly populations" Id. at page 310.
These studies have led to the recognition that there is a potential for fungal control of insects. However, no one has yet developed a consistent and commercially viable way of infecting insects and assuring that the fungi are dispersed throughout the breeding populations for the management and biological control of insects infesting houses or buildings.
It is therefore an object of the present invention to biologically control insects using entomopathogenic fungi.
It is a further object of the present invention to provide a device for the convenient, reliable and economically feasible application of fungi in the biological control of insects.
It is a further object of the present invention to provide a method and means for infecting all insects in a breeding colony by dissemination of a fungi pathogenic for insects.
It is another object of the present invention to provide a method and means for infection and killing of insects by a variety of fungi so that development of resistant strains is avoided.